EN 61000-3-3:1995

Limitation of voltage fluctuations and flicker in low-voltage supply systems for equipment with rated current <=16 A


This section is concerned with the limitation of voltage fluctuations and flicker impressed on the public low-voltage system.

It specifies limits of voltage changes which may be produced by an equipment tested under specified conditions and gives guidance on methods of assessment

This section is applicable to electrical and electronic equipment having an input current up to and including 16 A per phase and intended to be connected to public low-voltage distribution systems of between 220 V and 250 V at 50 Hz line to neutral

The test according to this section are type tests. Particular test conditions are given in annex A and the test circuit is show in figure1 of the standard.


  1. The limits in this section are based mainly on the subjective severity of the flicker imposed on the light from 230 V/60 W coiled-coil filament lamps by fluctuations of the supply voltage. For systems with nominal voltages less than 220V, line to neutral and/or frequency of 60 Hz, the limits and reference circuit values have not yet been considered.
    Special equipment which is not widely used and is designed in such a way that it is unable to comply with the requirements [limits] of this section may be subject to installation restrictions requiring the consent of the supply authority before connection.
  2. A guide to the assessment of such equipment is given in technical report IEC 1000-3-5.


voltage fluctuation: A series of voltage changes or a continuous variation of the r.m.s. voltage.
flicker: Impression of unsteadiness of visual sensation induced by a light stimulus whose luminance or spectral distribution fluctuates with time.
short-term flicker indicator, Pst: The flicker severity evaluated over a short period (in minutes); Pst = 1 is the conventional threshold of irritability.
long-term flicker indicator, Plt: The flicker severity evaluated over a long period (a few hours) using successive Pst values.


The limits shall be applicable to voltage fluctuations and flicker at the supply terminals of the equipment under test, measured or calculated according to clause 4 under test conditions described in clause 6 and annex A (in the standard). Tests made to prove the compliance with the limits are considered to be type tests.

The following limits apply:

bulletthe value of Pst shall not be greater than 1.0;
bulletthe value of Plt shall not be greater than 0.65;
bulletthe relative steady-state voltage change, dc, shall not exceed 3 %;
bulletthe maximum relative voltage change, dmax, shall not exceed 4 %;
bulletthe value of d(t) during a voltage change shall not exceed 3 % for more than 200ms.

If voltage changes are caused by manual switching or occur less frequently than once per hour, the Pst and Plt requirements shall not be applicable. The three requirements related to voltage changes shall be applicable with the previously mentioned voltage values, multiplied by a factor of 1.33.

The limits do not apply to emergency switching or emergency interruptions.

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Last modified: May 09, 2008